478 NEW YORK STATE MUSEUM 



varieties appear, strongly suggesting that one rock has been modi- 

 fied by incorporating material from the other. 



In the other direction the rock changes by increasing quartz. 

 The quartz also tends to appear in coarse leaves, or spindles, which 

 are very prominent on the weathered surface or in the hand speci- 

 men. The feldspar also changes slightly and tends to become red 

 instead of green producing green and red mottled rocks. Finally 

 the red predominates and the rock becomes a distinct granite. 



Basic syenite. This is in general a rather finely granular rock 

 of general black color but sufficiently coarse so that the com- 

 ponent minerals plainly show their proper colors to the eye. The 

 feldspar is usually brown, though it is green where fresh material 

 can be obtained. Garnet is in general not so prominent as in the 

 gabbro, and the rock tends to a finer and more even grain, but 

 the differences are slight. In general these basic rocks are con- 

 fined to the near vicinity of the anorthosite, though in the ordi- 

 nary syenite there is much variation from place to place in the 

 percentage of dark colored minerals. It will be later shown that, 

 even in thin section, it is very difhcult to distinguish these rocks 

 from the gabbros owing to the lack of distinctive features in the 

 feldspars, but that chemically they are easily separable. 



Granitic syenite. As mapped this comprises a mass of very 

 variable rock, much cut up by later granite, excellently exposed 

 in Litchfield park and in the two big ridges which run north from 

 it. Admirable exposures, often blasted, are found along the park 

 roadways. Much of the rock is alternately green and red, quite 

 quartzose, and a rock distinctly intermediate between syenite 

 and granite, often passing into granite. Much of it is uniformly 

 red, and the red rocks range from syenite to granite in composi- 

 tion. It is not certain that all these latter rocks are of the same 

 age, and differentiate in place of the main mass, and this is espe- 

 cially true of the red syenite. But it is certain that much of the 

 rock has this character, and the whole is manifestly bound to- 

 gether as a mass of eruptive material arising from a common 

 magma. It is all cut up by dikes and larger masses of a red granite, 

 mostly too small to map separately, a rock to be shortly described 

 as the Morris granite. 



Asymmetry of the syenite differentiation. The formation of a 

 gabbro border to the anorthosite by some not well understood 

 process of differentiation, has l^een seen to be a rather uniform 



